1. Field of the Invention
The present invention relates to low pressure chillers of chilled water or chilled brine refrigeration systems and, more particularly, to a method and apparatus for heating and pressurizing the refrigerant in such chillers during removal of fluids; during routine repair or maintenance when the machinery is not running; and, during testing for refrigerant leaks, thereby eliminating the loss of refrigerant (normally a fluoro-chloro hydrocarbon known as FREON.RTM.).
2. General Background
The chiller is the air-tight vessel component of a refrigeration system that contains the refrigerant solution which chills the transfer fluid (normally water) used for subsequent cooling purposes. Inside the chiller, this refrigerant solution is maintained at a very low pressure which results in a low temperature. Preferably, the pressure of the refrigerant (normally FREON.RTM. or, more particularly, R-11 or R-113) results in a vacuum so as to achieve low temperature. The transfer fluid circulates through this refrigerant solution within a serpentine coil until the desired temperature is reached. Afterwards, this transfer fluid is pumped to another location for refrigeration purposes.
In order to repair chillers, or check for leaks, it is necessary in many instances to either remove the refrigerant solution or raise it to ambient pressure. If neither is done, the possibility exists that air will be sucked into the low pressure chiller and mix with the refrigerant. If this happens, the refrigerant must be purged to eliminate the undesirable air. This is a time consuming and expensive operation that almost always results in the escape of a limited, although environmentally unacceptable, amount of refrigerant into the atmosphere. Approaching the problem from the temperature side--by attempting to directly heat a refrigerant such as FREON.RTM.--is unacceptable, as heating a refrigerant (such as R-11, R-12, R-22, R-113, R-500 or R-502) to a high enough temperature can cause "flashing" of the refrigerant which turns (it (changes state) to fosgene gas.
One method and apparatus for raising the pressure of the refrigerant inside the chiller to test for refrigerant leaks is disclosed in U.S. Pat. No. 4,862,698 to Morgan, et al. This patent discloses an auxiliary system (11) that couples to transfer fluid piping (19) outside of the chiller (15). Morgan, et al. '698 diverts this transfer fluid (20) (normally water) to a heater vessel (27) wherein its temperature is raised before being circulated within the cooling circuit (21) of chiller (evaporator) (15), thereby raising the temperature (and hence pressure) of the refrigerant (17) within the chiller (15). While this system will operate, its deficiencies include the fact that the temperature of the first heat transfer medium (liquid 20) is raised by a heat means 29 so that it can then raise the temperature of a second heat transfer medium (the refrigerant (17) within the chiller (15)). Thus, two separate heat exchange operations are required with each involving some degree of inefficiency. Applicants' apparatus and method has but one heat exchange operation, directly heating the refrigerant and increasing the efficiency of the unit. Morgan, et al. '698 will only work if the chilled water or transfer fluid is in the chiller piping (that is, that the chiller's cooling circuit is full of water). This heating of the water in the chiller's cooling circuit thus violates the chilled water circuit. Applicants' device works whether or not there is water or transfer fluid in the chiller's cooling circuit. This is particularly important in northern climates as many chillers are drained of their water and/or have their cooler or condenser heads removed in the cold weather. Morgan, et al. '698 also raises a broad spectrum of problems by having a chilled water diversion system in a high rise building where the pressure head on the chilled water or transfer fluid may reach 200 psi or more. Applicants' apparatus and method is connected to the refrigerant side of the system where the maximum pressure is 15 psi and operates at 18" vacuum to 8 psi (the oil side operates at 0 psi). Further, Morgan, et al. '698 can only heat the chilled water or transfer fluid in this system to its boiling point (212.degree. F. to about 250.degree. F.). Applicants' apparatus and method can heat the oil in the heat exchanger to about 400.degree. F., therefore, heating the refrigerant in the chiller much faster and reach 0 psi or a leak testing pressure much faster. Finally, Morgan, et al. '698 cannot be used to test cooler tubes or condenser tubes since the transfer fluid or water must be circulating to increase the temperature and pressure of the refrigerant.
A method and apparatus for electronically pressure sealing and leak testing an idle centrifugal chiller system are disclosed in U.S. Pat. No. 4,864,829 to Manning, et al. marketed under the name "PRE-VAC" by Mechanical Ingenuity Corp. Basically, Manning, et al. '829 uses the "blanket" approach--heaters glued to a shell, insulation and raising the temperature. A small positive differential pressure is electronically maintained between the interval refrigerant vessel pressure of the chiller system and the ambient atmosphere by selectively applying heat to the refrigerant. Manning, et al. '829 cannot be used on an exiting chiller unless the insulation is first removed, then Manning's device installed and then the insulation reapplied. If the insulation is rubber, Manning's device may melt the rubber or glue used to install the rubber insulation or start it burning. Most chillers come from the manufacturer installed with rubber. Manning's device is an electronic way of blanketing the chiller, whereas applicants' operation is manual. Further, Manning, et al. '829 is not portable.
A heated receiver control for refrigerant systems is disclosed in U.S. Pat. No. 3,238,737 to R. M. Shrader, et al. This device is for use with a high pressure refrigeration system and functions when the system is operating, not when the system is idle or "off." This device's primary use is with low ambient temperature and low load on a high pressure system. It is targeted to keep pressure drop across a metering device so that the system can operate under low load. If this device were heating vapor instead of liquid it could cause the refrigerant to "flash" and thus turn (change state) to fosgene gas. This is why the liquid is in the liquid receiver of the condensor.
U.S. Pat. Nos. 2,169,605 to Griese and No. 4,367,637 to Paulokat are representative of other, non-pertinent, refrigeration testing equipment.
It is thus an object of the present invention to provide a method and apparatus for raising the temperature of a refrigerant in a chiller without the deficiencies described above.
Another object of the present invention is to provide a method and apparatus that does not require two separate heat exchange operations to occur.
A further object of the present invention is to avoid the necessity of coupling to the transfer fluid piping and the need to raise the temperature of the transfer fluid in order to pressurize the refrigerant.
Still another object of the present invention is to provide a means for working on the chiller without the need to subsequently purge the refrigerant (because of its inadvertent mixing with air).
Still another object of the present invention is to reduce the leakage of refrigerant into the atmosphere which not only violates EPA regulations and potentially harms the environment, but also exposes the worker to potentially dangerous fosgene fumes.
still another object of the present invention is to raise the pressure of the refrigerant whether or not the chiller contains water in its cooling circuit.
Still another object of the present invention is to provide a means for pressurizing the chiller so as to allow for "leak testing."
Yet another object of the present invention is to allow leak testing when the chiller is idle or "off."
These and other objects will become obvious upon further investigation.